I follow chabad custom which, when it gets down to my hand, I believe involves only wrapping one finger of the hand in addition to the palm. I make the shin on my arm. But the Shema says bind it on your hand as a sign. So shouldn't there be a shin on my hand like in Ashkenazi custom?
"Yad" can also mean "arm." The "sign on your arm" that you're binding is the tefilin box on your bicep. You get the mitzva no matter which way you wrap the straps around your hand.